System for utilization of sinus-shaped motion pattern

ABSTRACT

The invention relates to a system for utilisation of a sinusoidal pattern of movement for propulsion or energy recovery. The system comprises a plurality of rigid hull elements, completely or partly submerged, arranged in a row, rotatably attached to one another for rotation about parallel axes of rotation across the longitudinal dimension of the row of hull elements. The system further comprises movement devices for rotating the hull elements relative to one another or movement devices for recovery of energy as a result of rotating the hull elements relative to one another.

[0001] The invention relates to a system for utilisation of a sinusoidalpattern of movement for propulsion or energy recovery.

[0002] Boats, ships, submarines, etc. are normally driven forward by themovement of a propeller or a water jet. The force that drives thesedevices is usually derived from a combustion engine, which has arepeating translatory movement that is converted to rotation by means ofa crank. In the present system of today, the losses occur both in themachinery and in the actual transmission to the water. All the currentpropeller solutions have a restricted speed window in which they areefficient. The principle behind propeller operation and water jets is togive a small volume of water a high velocity for propulsion of the boat,ship, etc. Another problem with the traditional propulsion system isthat there is inertia in the system and it has a relatively largeturning circle.

[0003] In order to achieve greater efficiency in propulsion machinery,attempts have been made to copy the pattern of movement ofwater-dwelling species. Examples of this are the imitation of thepattern of movement of a tuna fish, where the pattern of movementprovides propulsion for the automotive unit in U.S. Pat. No. 6,138,604.In this publication a freely swimming vessel is described with a rigidfront part and a flexible rear part. The front part has a given volumeand comprises a watertight chamber. The rear part has a smaller volumethan the front part and comprises manoeuvring and propulsion systems,where a power unit moves the rear part with a sinusoidal motion. For itspropulsion, a living tuna fish utilises movement of the body in a halfwavelength. The movement of the rear part of the vessel in U.S. Pat. No.6,138,604 is achieved by means of movement of hinged rigid rods by meansof hydraulic cylinders, where the rigid rods are connected in such afashion that they form a structure corresponding to a spine, in the rearpart of the vessel. The unit's rear part is made of a flexible material.This kind of flexible material is relatively expensive, and a structureof this kind is therefore not particularly suitable for largerdimensions. The vessel also has a “spine” of hinged rigid rods. Thiswill occupy a great deal of space in the vessel, thus making itunsuitable, for example, for transport purposes. The vessel is alsodesigned to exploit the pattern of movement in a half wavelength Anotherex-ample of a propulsion device like this is given in DE 301446, wherethe rear part of the fishlike structure consists of elements connectedwith a central “spine” for making the relative movements between theelements.

[0004] In JP 56157693 and JP 61278487 systems are disclosed forpropulsion of boats where the boats consist of several parts, which aremoved relative to one another for propulsion of the boat with rotationabout horizontal axes. With a boat design of this kind, wave motion,which is not caused by waves, will be felt on the deck of the boat, andthis is not particularly desirable.

[0005] For energy recovery of wave motion there are wave-power devicesconsisting of a mat-like structure that is floated on the surface of thewater. The mat-like structure consists of several articulated elements,which exploit relative rotational movement between the elements forgenerating energy. An example of this is described in EP 0035346.However, the utilization of wave energy is a fundamentally differentworking principle compared with the utilization of an energy in aunidirectional flowing fluid. In order to utilise underwater currentsand wind currents, rotating devices such as, for example, turbines aregenerally used for recovery of energy in the flowing fluid mass. Adrawback with these devices is that they usually have a relativelynarrow operational window in which they are effective, and if the flowrate is too low or too high, it will not be possible to use them. Forrecovery of energy in flowing bodies of water, such as wave power, thedevices also have to be capable of withstanding great-stress variations.

[0006] U.S. Pat. No. 5,740,750 describes a method and device forreducing the resistance for a body moving through a fluid. The body'spropulsion is preferably achieved by a propulsion foil attached to therear part of the body, but other known propulsion devices may also beemployed. Reduction of the resistance for the body is achieved byreducing the turbulence along the body. This is achieved by making atleast the rear third of the body flexible, thus causing it to set up alateral wave-like motion, with a wavelength between 0.0.5 and 2.0 timesthe length of the body. The aforementioned wave motion causes the waterpressure against the body to increase, thus maintaining laminar flowalong the body.

[0007] There are several problems associated with a solution like thatdescribed in U.S. Pat. No. 5,740,750. Where a foil is used that has atranslatory and rotating motion for creating propulsion, all forces haveto be absorbed in a small attachment point for the foil. Sincerelatively slow movements with a frequency of between 0.1 and 0.5 Hz areinvolved here, this means that enormous stresses will be created in thetransition between the body and the propulsion foil. A second problem isthat the body has to be tapered towards the rear in order to reduce thelateral forces, which otherwise would destroy the directional stabilityat wavelengths other than whole multiples of wavelengths. This gives thestructure a complicated shape with oval compartments that are difficultto use for stowing payload. Another problem is that in the solution inU.S. Pat. No. 5,740,750 an articulated skeleton structure (spine) isused, and covered by a flexible skin. This creates problems in caseswhere the structure requires to be scaled up, nor is the bodyparticularly suitable for deep water due to the pressure problem. Aspine also gives less space for stowing payload.

[0008] All these prior art systems have major drawbacks, there is theproblem with a central spine, which reduces the ability to stow cargo orother equipment, there is the problem with structures not adaptable toreally high pressures when utilizing the system at large water depths,there is also the problem with variable cross section over the length ofthe element which makes them more difficult to produce and use for cargoetc.

[0009] The object of the present invention is to provide a system forutilising a sinusoidal pattern of movement for propulsion or energyrecovery, where this is achieved by providing a device where thepropulsion or energy recovery are created by moving large volumes offluid at low speed in contrast to a more traditional propulsion devicewhere a small quantity of fluid is moved at high speed, which is theprinciple of a propeller. This will provide increased efficiency for thepropulsion or the energy recovery.

[0010] It is a further object to provide a device where the load onindividual parts is evenly distributed over the structure, and where theconstruction may have a substantially constant cross section along theentire length, with the result that the construction may consist oflinks essentially identical in shape, where it is easy to utilise thevolume since it does not change substantially over the length of thestructure.

[0011] Yet another object is to provide a device that can be scaled upin size, made watertight and used for higher pressure, in addition towhich the inner space in the structure can be used mainly for payload.

[0012] It is also an object of the present invention to provide adevice, which can easily be adapted in length for the applicationconcerned.

[0013] It is also an object of the present invention to provide a systemfor recovery of energy in a slow-flowing fluid that is more efficientthan traditional propeller systems.

[0014] The object of the invention is achieved by the features of thesystems set forth in independent claim 1 and independent claim 2.Additional features are set forth in the dependent claims.

[0015] The invention relates to a system for utilisation of a sinusoidalpattern of movement for propulsion or energy recovery, where the systemcomprises a plurality of rigid hull elements arranged in a row. The hullelements are rotatably interconnected for rotation about parallel axesof rotation across the length of the row of hull elements. The row ofhull elements may be completely or partly submerged depending on thearea of application for the row. A row of hull elements for energyrecovery from an ocean current will typically be completely submerged,but a surface ship may also be envisaged composed of the hull elementsaccording to the invention. In order to achieve propulsion the systemcomprises movement devices for rotating substantially the whole row ofhull elements relative to one another or as a reversed system themovement devices are employed for recovery of energy as a result ofrotation of substantially the whole row of hull elements relative to oneanother.

[0016] The system's sinusoidal pattern of movement is created by meansof angular change between the hull elements. The sinusoidal movement ispreferably created in a plane substantially parallel to the surface ofthe water and the row of hull elements forms a complete sinus wave.

[0017] In contrast to normal propulsion of a vessel by means of waterjet or propeller, the principle of which propulsion system is to move asmall quantity of water at high speed in order to achieve propulsion,the propulsion achieved with the present invention is obtained by movinglarge volumes of water slowly. This permits 85-90% of the energy toprovide propulsion while in normal propulsion systems, such as apropeller, the percentage is around 70.

[0018] Instead of generating propulsion, the system according to theinvention may be used in reverse for recovery of energy in a flowingfluid. It is precisely because the system is based on the movement oflarge volumes at low speed that it is suitable for recovery of energy influid flows, such as ocean currents. In the case of an ocean current,for example, the axis of rotation for the hull elements will preferablybe oriented substantially vertically.

[0019] The invention will now be explained with references toembodiments and drawings, in which:

[0020]FIG. 1 is a principle drawing of a row of hull elements, whichform a row according to the invention, viewed from the side.

[0021]FIG. 2 depicts principle drawings of a row of hull elementsaccording to the invention viewed from above, forming a straight and asinusoidal row.

[0022]FIG. 3 is a perspective view of a row of hull elementsconstituting a submerged vessel.

[0023]FIG. 4 is a principle drawing where the row of hull elementsaccording to the invention constitutes a vessel.

[0024]FIG. 5 depicts principle drawings where the row of hull elementsaccording to the invention constitutes a propulsion system for a vessel.

[0025]FIG. 6 is a principle drawing where the row of hull elementsaccording to the invention is employed as a power generator in a flowingfluid.

[0026]FIGS. 7-10 illustrate various embodiments of movement devices atthe links between the hull elements viewed from above.

[0027]FIG. 11 illustrates the solution indicated in FIG. 10 viewed fromthe side.

[0028]FIG. 12 illustrates an alternative embodiment of the movementdevices for the links between the hull elements viewed from above.

[0029] The invention relates to the utilisation of a sinusoidal patternof movement for propulsion or energy recovery. In order to utilise asinusoidal pattern of movement, a row of rigid hull elements areinterconnected. FIG. 1 illustrates an example of such hull elements 1assembled to form a row with a front hull element 11 and a rear hullelement, a tail 12. The hull elements 1 have rigid sides with an openspace inside, thus forming a shell structure. The hull elements asillustrated in FIGS. 1 and 2 are essentially rectangular, but othershapes may be envisaged. The cross sectional shape of the row across thelongitudinal dimension of the row may, for example, be more triangular,polygonal or oval, or alternatively circular or somewhat varied over thelength of the row. The hull elements have a width across the row, alength in the longitudinal direction of the row and a height in adirection substantially parallel with the axes of rotation.

[0030] The hull elements 1 are rotatably attached to one another forrotation about parallel axes of rotation across the longitudinaldimension of the row. Active rotation of the hull elements about theaxes of rotation is implemented by means of movement devices 2. When thehull elements are used for energy recovery, the rotating device at thelinks will convert the rotational energy to usable energy.

[0031] As illustrated in FIG. 2, rotation of the hull elements relativeto one another can give a sinusoidal shape to a centre line A drawnthrough the middle of the hull elements. By controlling the rotation ofthe hull elements, a repeating sinusoidal movement will be created overthe row of hull elements. The row of hull elements preferably forms acomplete sinus wave over its length. Controlling the angular changebetween the hull elements will also control the amplitude swing, i.e.the lateral movement of a point on the centre line A from the startingpoint, which is a straight centre line A. By this means equal amplitudecan be obtained for all points along the centre line A or the pointsalong the centre line A can have greater amplitude for the rear parts ofthe row and the greatest amplitude for the tail. This increase inamplitude swing may be linear or exponential. The last element in therow of hull elements 1, the tail 12, preferably has an oscillationamplitude corresponding to between 6 and 20% of the length of the row ofhull elements. The amplitude swings across the row are advantageously ±5degrees at the first link in the row of hull elements and ±30 degrees atthe last link in the row.

[0032] The number of hull elements in the row may be varied depending onthe area of application, where the row preferably comprises 2-10elements, a preferred number being 6-8. In the embodiment in FIGS. 1 and2 a row is illustrated with five hull elements.

[0033] The length of the hull elements may also be varied across therow, the front element 11 being the longest and the length subsequentlydecreasing towards the back of the row, either evenly distributed or ingroups. The tail in turn may be made longer.

[0034] This may be advantageous, for example, in cases where anexponential increase is required in the amplitude swing for the hullelements across the row.

[0035] The front hull element 11 in the row is generally more rounded atthe end facing the direction of travel or the direction of flow. Thefront hull element may also be in the form of the bow of a boat. Thelast element 12, the tail, may well be tapered in shape. This is inorder to obtain the best possible flow pattern round the propulsionsystem.

[0036] The connection between the hull elements may be implemented in anumber of ways with trunnions and grooves, hinges, pivots, etc. It isadvantageous to obtain an outer surface where there is a smoothtransition from the surface of one hull element to the surface of thesucceeding hull element. A smooth transition will have the leastpossible influence on the flow pattern round the row of hull elements.Such a transition can be achieved by means of the method of attachmentof the hull elements or by a more flexible cover over the link jointwhere one end of the cover is attached to a hull element, while theopposite side abuts against an adjacent hull element.

[0037] In FIG. 3 an embodiment of the invention is illustrated where therow of hull elements forms an autonomous vessel that operates underwater. Such a vessel will comprise at least one watertight chamber, andenergy for operating the movement devices will naturally come frombatteries or a motor. In such a vessel it will be natural to provide onemovement device for each link with a control unit, thus enabling thevessel to be moved in the desired direction, i.e. straight ahead,turning or turning around depending on the angular change between thehull elements. The hull elements in such a vessel will not bewatertight. Any equipment that is not waterproof can be placed inwatertight chambers. The vessel will also comprise buoyancy bodies,which may also be employed for vertical orientation of the vessel in thewater. Depending on the application, such a vessel will also be equippedwith sensors, storage media and possibly devices fortransmitting/receiving data to/from the surface. If it is expedient, thevessel may also be equipped with lines and transmission lines to thesurface and perhaps also extra propulsion machinery in the form of apropeller or the like.

[0038]FIG. 4 illustrates that the hull elements according to theinvention can also form a surface vessel.

[0039]FIG. 5 illustrates that the hull elements according to theinvention can form the propulsion mechanism for a vessel. In this casethe row of hull elements is attached rotatably to the vessel under therear half, with the result that, when the hull elements are given asinusoidal pattern of movement, this movement drives the vesselforwards. If the row of hull elements is rotatably attached to thevessel, the whole row can be rotated in order to rotate the vessel'sdirection of travel, instead of it being the relative angulardifferences between the hull elements that rotate the vessel. The row ofhull elements may be located under or behind the vessel, or for acatamaran, for example, between the hulls. With regard to runningaground and bringing into dock, etc., it is desirable for the row ofhull elements to be arranged over a bottom line for the vessel's hulland within the extremities of the hull. It may also be envisaged thatother propulsion equipment such as a propeller may be installed on thevessel.

[0040] In FIG. 6 an embodiment is illustrated where a sinusoidal patternof movement for the row of hull elements is used for recovery of energyfrom a fluid flow. Such a fluid flow, where the fluid is water, may be atidal flow, the mouth of a river, flows resulting from waves or oceancurrents. In the embodiment in FIG. 6 the front hull element 11 isattached to a movable anchor point by mooring lines 5 and a buoy 4.

[0041] In this embodiment the row of hull elements consists of nine hullelements. The pattern of movement of the hull elements creates a sinuswave in a substantially horizontal plane. In this embodiment forrecovery of energy, the hull elements, which have a width across the rowin a substantially horizontal direction, a length in the longitudinaldirection of the row and a height across the row in a substantiallyvertical direction, have been given a minimal width and a height greaterthan the length. This is to ensure that they occupy as little space aspossible in the water flow while receiving the greatest possibleinfluence from the water flow.

[0042] The invention employed for recovery of energy in a flowing fluidmay be designed in several ways. The first element in the row may besecurely anchored to the bottom by an anchor chain, a post or othersuitable installation, or, for example, to a floating platform, asubmerged buoy or a cement foundation on the bottom. The hull elementsthemselves can provide the buoyancy for the device and/or it may havebuoyancy chambers when it is placed in water. Alternatively or inaddition, the hull elements may be weighted if they are anchored, forexample, to a submerged buoy. The device may also be envisaged placed ina fluid flow where the fluid is a gas such as air. In this case theweight of hull elements and movement devices becomes a crucial factor.

[0043] The movement device which influences or is influenced by theangular change between the hull elements in the row may be designed inmany different ways. Some of these designs are illustrated in FIGS.7-12. These movement devices are adapted in such a manner that they aresupplied with energy in order to establish angular changes between thehull elements when the row of hull elements has to create propulsion orthey can generate energy as a result of angular changes when the row ofhull elements is used for energy recovery. The energy supplied to themovement device may come from a suitable source depending on the use ofthe system.

[0044] In FIG. 7 movement devices are illustrated consisting of pistons21, piston cylinders 22 and transmission arms 23. At a link 2 a betweentwo hull elements 1, on each side of the link with the axis of rotation,there is placed a piston with piston cylinder and transmission arm,where the piston cylinder with the piston working within it is attachedto one hull element and where the transmission arm is rotatably attachedto the piston and the second hull element. On adjustment of the pistons'position in the piston cylinder, this offers the possibility ofadjusting the angular motion between the two hull elements. The pistoncylinders with pistons may be single or double acting. In the case ofdouble-acting pistons the movement device may consist of only onepiston/piston cylinder. For recovery of energy, the movement of thepistons in the piston cylinders as a result of the angular change isemployed for generating energy.

[0045] In FIG. 8, a second embodiment of the movement device isillustrated, consisting of a motor 25, an eccentric arm 26 and atransmission arm 23. The motor is of any suitable type and has theeccentric arm 26 mounted in its point of rotation. The transmission arm23 is rotatably attached to the eccentric arm 26 at a distance from theeccentric arm's 23 point of rotation. By controlling the motor'srotation, control can be achieved of the angular change between the hullelements. By means of externally applied angular change between the hullelements, it will be possible to generate energy as a result of theeccentric arm's 26 rotational motion.

[0046] A further embodiment of the movement device is illustrated inFIG. 9. In this embodiment the movement device consists of two bellows27 arranged on each side of the link between two hull elements 1. Thebellows 27 and lateral surfaces in the two hull elements form a pressurechamber 28, which is connected, for example, to a two-way pump 29. Byregulating the pump and thereby the pressure in the two pressurechambers on each side of the link, the angular change between the hullelements can be regulated. In the case of energy recovery, instead of apump, a turbine or other equipment for recovery of energy may beprovided which employ the altering of the pressure differences betweenthe two chambers.

[0047] A further example of a movement device is illustrated in FIGS. 10and 11, where FIG. 11 illustrates the device in FIG. 10 viewed from theside. The movement device in this embodiment consists of a motor 25, awire 24 and four castors 24A. By placing the wire over the castors insuch a manner that movement of the wire 24 by means of the motor 25 inone direction results in angular displacement between the hull elementsin one direction, and conversely for angular change in the otherdirection, adjustable angular change can be obtained between the hullelements. Instead of wire the use may be envisaged of other elongatedelements such as a chain, etc. A different number of castors may also beenvisaged. The position of the castors will depend on the number anddesired relative movement of the wire 24 in relation to the angulardisplacement between the hull elements. For energy recovery, the wiremovement generates energy.

[0048] As an alternative to the above-mentioned examples, the use may beenvisaged of toothed wheel transmission for the movement device forregulating the angular motion between the hull elements.

[0049] In FIG. 12 there is illustrated a movement device, which may beemployed in cases where a predetermined angular change is requiredbetween the different hull elements in the row. Such an embodiment ofthe movement device 2 may be employed, for example, when the row of hullelements 1 is required to create propulsion straight ahead, or energyrecovery in a steady fluid flow. The movement device 2 consists of amotor 30 located at the front link 11. The motor 30 has an eccentric arm31 mounted in a point of rotation. Furthermore, several wires 32 aremounted at a distance from the eccentric arm's 31 point of rotation.There is a wire 32 for each hull element 1 in the row after the firsthull element 11. From the mounting point in the eccentric arm 31, thewires 32 are each passed through a phase guide 33, where the phaseguides 33, 33′ are located at regular angular distances in a 360 degreecircle round the motor 30 and the eccentric arm 31. From the phase guide33 the wire 32 is passed to the link between the two hull elements 1that it is intended to regulate. At the link the wire 32 is arranged ina guide 34 on the front hull element 1 in the link and attached to afastening device 35 on the second hull element 1. The angular movementbetween all the hull elements in the row can thereby be regulated bymeans of a motor, or energy can be generated from the angular change ofall the hull elements.

[0050] The invention is explained in the above with reference toembodiments. A number of other variants may be envisaged within thescope of the invention as it is defined in the following claims. Motorsfor implementing angular change between the hull elements may be anysuitable type of motor. It may also consist of a unit that converts theelectricity from batteries to rotational energy for rotation of theeccentric arm. The row of hull elements for recovery of energy in aflowing fluid may, for example, be attached to anchor chains or a signalbuoy mooring where the generated energy is transferred to batteriesprovided in the surface buoy.

1-8. (cancelled)
 9. A system for utilisation of a sinusoidal pattern ofmovement for propulsion comprising a plurality of rigid hull elements(1), completely or partly submerged, arranged in a row, rotatablyinterconnected for rotation about parallel axes of rotation across thelongitudinal direction of the row of hull elements, and movement devices(2) for rotating substantially the whole row of hull elements relativeto one another, wherein the row of hull elements (1) comprises a vessel(3) or is rotatably attached to the vessel (3), and wherein one or moreof the hull elements (1) comprise a watertight chamber, and whereinenergy for operating the movement devices (2) is provided by an internalcombustion engine and/or battery, whereby propulsion of the vessel (3)is achieved completely or partly by induced rotation of the hullelements (1) relative to one another, and further wherein the sinusoidalpattern of movement is created by means of angular changes between thehull elements (1) and is in a plane substantially parallel to thesurface of the water, and that the row of hull elements (1) forms acomplete sinus wave, and the row comprises at least 4 hull elements (1)behind one another and that the hull elements have a substantiallyconstant cross sectional area over the length of the row of hullelements, and where the hull elements (1) have rigid sides with an openspace inside, thus forming a shell structure.
 10. A system according toclaim 9, wherein the amplitude of the sinusoidal pattern of movementthat is created by the angular change between the hull elementsincreases linearly or exponentially over the length of the row of hullelements (1).
 11. A system according t-o claim 10, wherein the last hullelement (1) in the row, the tail (12), preferably has an oscillationamplitude of 6-20% of the length of the row of hull elements.
 12. Asystem according to claim 11, characterised in that the movement device(2) comprises hydraulic and/or gas cylinders and/or a motor with powertransmission devices at each connecting link between the hull elementsfor controlled angular motion between the hull elements or recovery ofenergy.
 13. A system according to claim 11, characterised in that themovement device (2) comprises an eccentrically mounted motor at thefront hull element and connection lines to the succeeding hull elementsfor fixed controlled angular motion between, the hull elements orrecovery of energy.
 14. A system according to claim 11, characterised inthat the movement device (2) comprises chambers for each connecting linkarranged at two opposite sides of the connecting link, fluid connectionsbetween the chambers including valves, a motor and/or a pump and controlsystem for control of valves and motor/pump.
 15. A system forutilisation of a sinusoidal pattern of movement for energy recovery,comprising a plurality of rigid hull elements (1), completely or partlysubmerged, arranged in a row, rotatably interconnected for rotationabout parallel axes of rotation across the longitudinal direction of therow of hull elements, and movement devices (2) for recovery of energy asa result of rotation of substantially the whole row of hull elementsrelative to one another, wherein the row of hull elements (1) is locatedin a substantially unidirectionally flowing fluid, the first hullelement (1) is anchored to a stable unit, the other hull elements (1)are floating freely in the fluid flow, whereby on movement of the hullelements (1) relative to one another, the movement devices (2) convertthis motion to energy, which can be transferred from the hull elements(1) to an operational site and/or supply network, and further whereinthe sinusoidal pattern of movement is created by means of angularchanges between the hull elements (1) and is in a plane substantiallyparallel to the surface of the water and that the row of hull elements(1) forms a complete sinus wave, and the row comprises at least 4 hullelements (1) behind one another and that the hull elements have asubstantially constant cross sectional area over the length of the rowof hull elements, and where the hull elements (1) have rigid sides withan open space inside, thus forming a shell structure.
 16. A systemaccording to claim 15, wherein at least one of the hull elements has abuoyancy unit and/or a weight unit.
 17. A system according to claim 16,wherein the amplitude of the sinusoidal pattern of movement that iscreated by the angular change between the hull elements increaseslinearly or exponentially over the length of the row of hull elements(1).
 18. A system according to claim 17, wherein the last hull element(1) in the row, the tail (12), preferably has an oscillation amplitudeof 6-20% of the length of the row of hull elements.
 19. A systemaccording to claim 18, characterised in that the movement device (2)comprises hydraulic and/or gas cylinders and/or a motor with powertransmission devices at each connecting link between the hull elementsfor controlled angular motion between the hull elements or recovery ofenergy.
 20. A system according to claim 18, characterised in that themovement device (2) comprises an eccentrically mounted motor at thefront hull element and connection lines to the succeeding hull elementsfor fixed controlled angular motion between the hull elements orrecovery of energy.
 21. A system according to claim 18, characterised inthat the movement device (2) comprises chambers for each connecting linkarranged at two opposite sides of the connecting link, fluid connectionsbetween the chambers including valves, a motor and/or a pump and controlsystem for control of valves and motor/pump.